1. Field of Invention
The present invention relates to microfabricated and microfluidic structures. In one example, the present invention relates to a microfabricated system and method for genome sequencing.
2. Description of Related Art
The cross-injector is utilized in nearly all academic and commercial microfabricated capillary electrophoresis (μCE) applications to form small, well-defined sample plugs. FIG. 1 shows a simple schematic of a cross-injection system used in microdevices. In FIG. 1, injection channel 109 is connected to sample reservoir 101 and sample waste reservoir 103. Separation channel 111 has buffer inlet reservoir 105 and buffer outlet reservoir 107. Electrodes are associated with reservoirs 101, 103, 105 and 107. In operation, a sample containing an unpurified analyte, e.g., DNA, is placed in the sample reservoir 101 and an electric potential is applied between the sample reservoir 101 and the waste reservoir 103. A sample is drawn from the sample reservoir 101 across the injection channel 109. By controlling the voltage across the injection and separation channels, a sample plug can be formed at the intersection 113 of the channels. The sample plug is then injected into the separation channel 111 by applying a potential across the separation channel, between reservoirs 105 and 107. In this manner, a sample is injected into the separation channel. Using the cross-injector, however, an excess sample volume is necessary to form and inject the sample plug. In addition, without desalting, the sample plug will contain ionic buffer and other ionic reagents. Because of these factors, cross-injector systems have efficiencies of 1% or less.
In advanced integrated microdevice systems that seek to miniaturize not only CE but all processing steps, the cross-injector is a barrier to reaching theoretical miniaturization limits. Additionally, cross-injection timing requirements can hinder optimization of array CE microdevices and integrated bioprocessor systems operating on limiting amounts of template. T-injection designs also present requirements that have similar barriers to miniaturization and timing optimization. Direct analyte injection that has been used in certain CE applications yields low-resolution, low-sensitivity separations due to the large sample plug size and injection of contaminants that are not suitable for applications such as Sanger DNA sequencing.